No. In the brain, neurons have many dendrites. They usually branch 4-5 times. “Segments” are the distances of dendrites between these branches. The dendritic segments between the cell body and the first branch are proximal. The others segments past that first segment are distal. So in the brain, there are many proximal dendritic segments (4-5 usually, I think).
In NuPIC, we do not model multiple proximal dendritic segments. We model only one, because we haven’t needed more than one for HTM theory to work, and we’re just trying to keep it simple. Distal segments are another story, however. We must have many distal segments.
There may come a time in the future, or a type of input, where we’ll need multiple proximal dendritic segments. Who knows?
The answer is we don’t know. HTM is a theory of intelligence based on what we do know, but this is theory, and theory is otherwise known as “our best possible guess”. It looks to me very possible that cortical layers are getting joined input / split output, and it not only makes sense but opens up lots of doors to postulate new ideas about how layers work together to represent reality. The idea that grid cells can represent complex locations using properties of SDRs allows us to think of our brains’ job differently, and gives us ideas about how perception turns into memory.
We try to model what we think pyramidal neurons in the brain do, which is grow dendritic segments and axons to meet each other. We model this by creating a randomly initialized network of cells that are somewhat connected. The SP has mini-columns that are randomly connected to the input. Some synapses are connected, others are not, but might be soon. Once the SP starts running I don’t think it will grow new segments or synapses, but existing synapses can become more/less permanent. In the distal connections things are much more fluid. I don’t think we start anything connected to another, we just let input come in and distal segments/synapses will start growing between cells as spatial patterns are processed. I really don’t know if this is how it works in the brain (I am not a neuroscientist), but this is the best way I understand the logic of HTM.
I’m not sure what you mean with this question. Spatial pooling is what we think is happening in the brain, in at least two layers of cortex. I think it is important to process sensory input with spatial pooling, which allows all sensory input to be uploaded into a common format, one that can be comparable to others.